Pigeons match primates in number sense

A group of scientists find that pigeons are capable of learning a simple …

By now, we all know that being called a "birdbrain" isn’t really an insult; birds have been shown to have several higher-order cognitive skills that we previously thought only primates had the brains for. Jays are capable of episodic memory, parrots can solve multi-step puzzles and use a succession of tools to get a food item, and crows have even learned to use city traffic and stoplights to their advantage. Now, Science reports yet another cognitive area where birds are on par with primates: they have a sense of numbers.

In 1998, a pair of researchers used a novel experiment to show that rhesus monkeys had numerical competence; in other words, they could use abstract numerical rules. The monkeys were shown a set of three images picturing one, two, and three items, and were trained to choose these images in ascending order. Once they had been trained to a certain accuracy level, they were shown numbers of items that they hadn’t necessarily seen before. The monkeys were generally able to choose the greater of the two numbers, even when they didn’t have experience with the values involved. Clearly, they had learned not only the values they were trained on, but also more abstract rules about numerosity.

The authors of this week’s Science article tested pigeons in the same way. They were taught to order 35 different sets of images, all of which displayed one, two, or three items. Then, the setup changed: values up to nine were introduced. The pigeons were then shown a pair of two familiar numbers (such as two and three), one familiar and one unfamiliar number (such as one and seven), or two unfamiliar numbers (such as five and eight).

Not surprisingly, the pigeons did well at the task comparing two numbers they had been trained on. However, they also performed very well on the other two tasks, choosing the greater number in more than 90 percent of the trials with the familiar-novel pairs, and about 75 percent of the time in the trials with the novel-novel pairs. The pigeons’ accuracy was lowest when the distance between the two numbers was small and when the ratio of the numbers was close to 1.

Overall, the birds performed about as well as the rhesus monkeys had in the original experiment. Both species are certainly capable of learning a simple mathematical rule, then using that rule in a more abstract sense to handle new values. So the obvious question now is whether the two species share a common ancestor with a keen number sense, or whether they both acquired their numerical competence through convergent evolution. Unfortunately, as the answer so often is in science, we don’t know yet.

Kate Shaw Yoshida
Kate is a science writer for Ars Technica. She recently earned a dual Ph.D. in Zoology and Ecology, Evolutionary Biology and Behavior from Michigan State University, studying the social behavior of wild spotted hyenas. Emailkate.shaw@arstechnica.com//Twitter@KateYoshida

31 Reader Comments

So the obvious question now is whether the two species share a common ancestor with a keen number sense, or whether they both acquired their numerical competence through convergent evolution. Unfortunately, as the answer so often is in science, we don’t know yet.

I don't know... I'd be tempted to believe that the ability to determine 'more' might exist outside of a sense of numerosity.

A bird confronted with two piles of bird seed - one big and one small - should go for the big pile, but it isn't necessarily due to an understanding that the big pile has a higher count of seeds in it.

The problem with using 2D images is, the pigeons are not necessarily really counting or numerically estimating the number of objects and comparing the quantity in abstract. They may as well be relating to the amount of brightness from the monitors for example, a screen with more objects in display appear brighter. That I wouldn't say is a hard task for a neuro network of several million neurons.

When we do know it, the reality is likely to be something along these lines. Human beings construct a cognitive model both of our self and of our external world. This model has a physical reality that is yet to be understood. The evolutionary history of the development of this model is rooted in the common evolutionary history of all bilateral metazoan animals. The root model is in turn rooted in the common history of evolution of eukaryotic cells. The fundamental structure of our model of the external world is largely based on some kind of physical representation of the objects in front of our eyes. The ability to enumerate and classify our abstract representation of those objects is basic to our cognition. So are the concepts of more and less. It is quite possible that there will turn out to be some significant differences between mammals and birds. Some convergent evolution could have taken place between different elements created on top of a common base. But the main distinctions in human cognition are likely to be largely a function of two factors. One is simply the ability to create substantially more detailed and refined models. The other is a recursive process that has developed specifically in the human line of evolution that allows us to build an additional physical model that maps to our use of words by reflecting on the more basic model that we share with other mammals and probably at some level with all other bilateral metazoan organisms.

The problem with using 2D images is, the pigeons are not necessarily really counting or numerically estimating the number of objects and comparing the quantity in abstract. They may as well be relating to the amount of brightness from the monitors for example, a screen with more objects in display appear brighter.

You could control for that (and perhaps the scientists did) by having some image pairs show light objects on a dark background while others show dark objects on a light background. If the pigeons' accuracy is unchanged then it's very likely that they're processing the number of items.

I don't know... I'd be tempted to believe that the ability to determine 'more' might exist outside of a sense of numerosity.

A bird confronted with two piles of bird seed - one big and one small - should go for the big pile, but it isn't necessarily due to an understanding that the big pile has a higher count of seeds in it.

Very interesting research, nonetheless.

You can control for this by having fewer, larger dots on some slides. If they can tell the difference between smaller dots encompassing the same area as fewer larger dots you know they aren't just determining less / more by aggregate size.

I don't know... I'd be tempted to believe that the ability to determine 'more' might exist outside of a sense of numerosity.

A bird confronted with two piles of bird seed - one big and one small - should go for the big pile, but it isn't necessarily due to an understanding that the big pile has a higher count of seeds in it.

Very interesting research, nonetheless.

You can control for this by having fewer, larger dots on some slides. If they can tell the difference between smaller dots encompassing the same area as fewer larger dots you know they aren't just determining less / more by aggregate size.

Exactly. I was reading about a similar study with dogs a few years ago. Up to something like seven items, dogs will pick the slide that has more items (pick six small circles over five big circles). Past that, they will pick the slide where the items cover the largest area (pick eight big circles over nine small circles).

You could imagine that, escpecially for social animals, it could be beneficial to have a sense of greater/fewer when dealing with a small number of items -- for instance, is that competitive pack of dogs smaller or bigger than my pack. But for larger groups of items, area/volume might be more useful -- for instance, which bowl has more dog food in it.

This just in: Everytime we study more and more animals we realize they're quite smart. What a marvel of human innovation to determine that an animal (Which takes care of itself, walks, makes noises and MUST think to survive) can solve basic Math problems, dear god! Call me shocked.

In other news: Do we need oxygen to breathe? Studies are finding that yes, oxy . . .

This just in: Everytime we study more and more animals we realize they're quite smart. What a marvel of human innovation to determine that an animal (Which takes care of itself, walks, makes noises and MUST think to survive) can solve basic Math problems, dear god! Call me shocked.

For a very long time people thought that cognitive reasoning was a special ability.

There have been extensive studies of the mental abilities of corvids (ravens and crows and such) and they were also shown to have surprising abilities. If a crow watches three hunters enter a hunting blind it will realize the area is safe until all three hunters have left the blind. Studies even suggest that the corvids are actually on par with the great apes cognitive abilities.

There have been extensive studies of the mental abilities of corvids (ravens and crows and such) and they were also shown to have surprising abilities. If a crow watches three hunters enter a hunting blind it will realize the area is safe until all three hunters have left the blind. Studies even suggest that the corvids are actually on par with the great apes cognitive abilities.

Safe as in hunting some other kind of bird?

sniii wrote:

Sharing a common ancestor seems a bit far fetched. There would be about 100,000,000 years of divergence between the two.

This just in: Everytime we study more and more animals we realize they're quite smart. What a marvel of human innovation to determine that an animal (Which takes care of itself, walks, makes noises and MUST think to survive) can solve basic Math problems, dear god! Call me shocked.

For a very long time people thought that cognitive reasoning was a special ability.

Quite true. After looking at not only studies on the cognitive skills of animals, and humans, but also comparisons of cognitive fallacies, I've personally come to the conclusion that animals are far smarter than we though, and that we humans are not quite as smarts as we'd like to believe either. Then again, these kinds of cognitive biases are just one of a long list of common fallacies.

My old housemate's Dad (MIT professor) told me how they figured out birds can "count" up to 4. They added eggs to a bird's nest while the bird was away. If the starting number of eggs was 4 or below, the bird would refuse to sit the nest if the number had changed.

If the starting number was higher than 4, they could add as many eggs as they wanted to, and the bird would sit.

The rabbits of Watership Down were similarly limited, having the numbering system of 1, 2, 3, 4, "Hrair", where the latter translates variously as "thousand" or "infinity."

Do we have any way of knowing whether there is only one way for brains to do "number sense" (hence primates and birds either sharing a common ancestor or undergoing convergent evolution), or whether "number sense" is an emergent trait potentially achievable through a wide variety of brain structures?

In other words, it seems we know that being smart at many different things leads one to also be smart with numbers. But do we know that being smart with numbers is also indicative of being smart with many different other things?

In other words, it seems we know that being smart at many different things leads one to also be smart with numbers. But do we know that being smart with numbers is also indicative of being smart with many different other things?

It might not tell much by itself, but I think it says more when included with past cognitive studies.

Here's something interesting to think about. Birds have dramatically smaller brains than mammals. Has evolution found a more efficient way to shoehorn these abilities into a smaller space? or do their brains lack certain other functions that mammals have?

The idea of a common ancestor with 'numerosity' would surely be coincidental. For it to have any relevance you would need to check all of the ancestors on both lines going back to the original concestor (using Dawkins' terminology for the first ancestor that is common to both lines) for numerical skills.

There are plenty of documented examples where animals have evolved traits and then lost them over time according to natural selection. There are bats in New Zealand that - having gained flight - have largely lost it and now crawl on forest floors with wings. There are underground mammals that have vestiges of eyes that are no longer used. Yes these are physically tangible traits, but numerosity is likely a consequence of particular evolutionary traits in an animal's brain - some will have it while others won't.

I did notice the authors mentioned that the pigeons struggled with numbers with a ratio close to 1. Is this indicative that the pigeons are looking more at magnitude or size of the 'collection', as opposed to the number? I'd be interested to know if they did a comparison with say one large dot, two smaller dots, and then four very small dots with an area lower than the original dot. How would the pigeon react then?

Quote:The monkeys were shown a set of three images picturing one, two, and three items, and were trained to choose these images in ascending order. Once they had been trained to a certain accuracy level, they were shown numbers of items that they hadn’t necessarily seen before. The monkeys were generally able to choose the greater of the two numbers, even when they didn’t have experience with the values involved.

I don't know... I'd be tempted to believe that the ability to determine 'more' might exist outside of a sense of numerosity.

A bird confronted with two piles of bird seed - one big and one small - should go for the big pile, but it isn't necessarily due to an understanding that the big pile has a higher count of seeds in it.

Very interesting research, nonetheless.

And if the smaller pile has a greater number of smaller seeds, and the bird still picks it, then it has number sense.

Pigeons also seem able to grasp quite abstract concepts in visual object recognition (recognising e.g. "water", be it a picture of water in a glass or one of sun setting over the ocean -that kind of thing anyway). If I recal correctly they outperform humans on some such tasks.

fjellfras wrote:

So machine learning can be replaced by monkey learning ?

Parralel distributed processing / "connectionist" modeling is an increasingly dominant approach in cognitive science, aand it more or less ammounts to a type of machine learning. Connection weights are randomised, then adjusted in response to "correct" outputs, then randomised, etc., until the network learns to generalise. So maybe machine learning and monkey learing are the same thing?

Perhaps there are multiple avenues for the brain to determine size/amount computations. Just because we as humans have a highly developed sense of numbers its only after running through several highly evolved modules that are modern in the mammal/human brain.

for instance your body will automatically dodge any item that it perceives as being a danger even before the higher level cognitive part of the brain reacts to exactly what the object is. Point being...understanding the object is not as important in evolution as understanding the danger so we have a low level response that triggers physical reaction before we have time for our neocortex to fully process. The same thing that drives that flinch is something that evolved early (and is shared in much of the animal kingdom) but being able to recognize that item as a baseball is a much later development in evolution.

perhaps the same thing is true for other higher function vs lower function brain processes...just because we process things differently doesnt mean other animals may not have a similar less adapt functionality in the lower levels of the brain.

This just in: Everytime we study more and more animals we realize they're quite smart. What a marvel of human innovation to determine that an animal (Which takes care of itself, walks, makes noises and MUST think to survive) can solve basic Math problems, dear god! Call me shocked.

Another one of these statements that I heard recently was that humans are the only species aware of their own mortality. No idea what convoluted logic was used to arrive at that conclusion. Some humans like to think they're so special, I guess.

Perhaps it's because some people mistake the concept of something with the something itself and think that therefore, if other animals can't communicate a conceptual understanding of something that it means they don't have any understanding.